Metal-clad, compressed-gas insulated, high-voltage switching station with an insulated grounding switch

ABSTRACT

A metal-clad, compressed-gas insulated, high-voltage switching station with an insulated grounding switch. In the case of compressed-gas insulated, high-voltage switching stations, insulated grounding switches are also used for applying test voltages. Therefore, provided between the housing and the casing is an insulating ring, within which a conductor is embedded with a terminal lug which contacts the contact pin. In order to improve the insulation, the insulating ring reposes within a metallic ring, which acts as a prop ring and which receives the fixing agents. It is only interrupted by the terminal lug which is provided with an insulating enclosure. The insulating ring is thus largely relieved from mechanical stresses. Insulated grounding switches are used in the case of metal-clad, high-voltage switching stations which are insulated by SF 6  compressed gas.

BACKGROUND OF THE INVENTION

The invention relates to a metal-clad, compressed-gas insulated,high-voltage switching station with an insulated grounding switch whosehousing is flange-mounted to the casing of the high-voltage switchingstation by way of flanges and fixing agents which connect these flanges,whereby one insulating ring is mounted gastight between both flanges. Onthe inside of this insulating ring, an annular electric conductor, whichis provided with a terminal lug, is embedded such that the terminal lugwhich runs outside passes radially through the insulating ring, and theannular part of the conductor surrounds the contact pin of the groundingswitch with clearance, whereby the conductor bears a sliding contact byway of which it is electrically connected to the contact pin.

This type of an insulated grounding switch for a metal-clad,compressed-gas insulated, high-voltage switching station is known fromthe teachings of U.S. Pat. No. 3,778,374. The conductor, with theterminal lug running to the outside, which is embedded in the insulatingring can be either grounded via this grounding switch or a voltage canbe applied to it which is then transferred to the contact pin of thegrounding switch in order to implement testing. In the known groundingswitch, the annular part of the conductor is embedded on the inside ofthe insulating ring. This insulating ring reposes between the flange ofthe housing of the grounding switch and the flange of the casing of thehigh voltage switching station and is penetrated by the fixing agentswhich serve to fasten the grounding switch to the high voltage switchingstation. In this manner, the insulating ring is pressurized by thecompression forces required for fastening it and is thereby mechanicallystressed by high compressive forces.

Consequently, the tightening torques for the fixing agents must bestipulated precisely and with a narrow tolerance range in order to avoidoverloading the insulating material. Furthermore, the fixing agents mustbe provided with an insulation since they are located in the immediatevicinity of the embedded conductor and are connected to the groundedcasing. The entire outer surface area of the insulating ring isfurthermore exposed. In the case of outdoor use, this can createproblems since then the insulating property of the insulating ring canbe impaired by deposits.

SUMMARY OF THE INVENTION

The invention is based on the task of improving the insulation of thegrounding switch in the case of a metal-clad, compressed-gas insulated,high-voltage switching station of the initially described type.

In order to solve this task in the case of a metal-clad, compressed-gasinsulated, high-voltage switching station with an insulated groundingswitch according to the invention, the insulating ring reposes within ametallic ring of at least the same height and with this metallic ring ismounted gastight between both flanges. The metallic ring has a radiallydirected opening through which the terminal lug, which is provided withan insulating enclosure, extends, and the fixing agents penetrate onlythe outer metallic ring.

For the insulating ring, the outer metallic ring acts as a prop ring,which encloses the insulating ring on the entire outer surface area.Only at one spot on the periphery does it have an opening, which,however, does not extend through its entire height and which ispenetrated but not interrupted by the insulated andgastightly projectingterminal lug. Thus, there is always a metallic connection between thehousing of the grounding switch and the casing regardless of whether thegrounding switch is being used for grounding or for test purposes. Thefixing agents are only run through metallic parts and do not require aseparate insulation. Moreover, in this manner, a precise insulatingclearance is guaranteed between the mounting flanges as well as adefined packed sealing gap between the flange and the ring,respectively.

The forces required for fastening are absorbed only by the metal parts.The insulating ring is only stressed by the compressive forces of thesealing ring and therefore is subjected to only low mechanical stresses.Furthermore, since only the thin-walled insulating enclosure whichsurrounds the terminal lug leads outside, this design is also wellsuited for high-voltage switching stations which are located outdoors.

It is particularly advantageous when the insulating ring consists ofcured cast resin. In this case, the outer metallic ring can be used aspart of the requisite casting mold, within which the electric conductoralong with the terminal lug are inserted and retained with theappropriate clearance. The embedding of the conductor thus takes placeduring casting, and the molding compound then forms the insulating ringand the insulating enclosure of the terminal lug after curing. Duringcuring, furthermore, there is the advantage that the cast resin shrinksonto the terminal lug and thus forms a gastight connection there.Therefore, no special additional measures are required in order toproduce the gastightness between the terminal lug and the insulatingring. The gastight sealing of the end faces of the insulating ring tothe adjacent end faces of the flanges takes place in the usual mannerwith the aid of sealing rings.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention is more closely explained in the following in light of theexemplified embodiment which is represented in FIGS. 1 and 2 of thedrawing, however, to which exemplified embodiment the invention is notrestricted. In a schematic representation,

FIG. 1 shows the part of a longitudinal section through a metal-clad,compressed-gas insulated, high-voltage switching station with aninsulated grounding switch.

In FIG. 2, the section II--II in FIG. 1 is represented.

DETAILED DESCRIPTION

In the case of a metal-clad, high-voltage switching station which isinsulated with compressed gas, in particular with SF₆, a conductor 2carrying high voltage, which can be grounded by means of a groundingswitch 3, is mounted within a casing 1. For this purpose, the conductor2 has the counter contact 4 for the contact pin 5 of the groundingswitch 3, which contact pin 5 is moved by a driving mechanism not shownand which can be engaged with the counter contact 4.

The housing 6 of the grounding switch 3 ends in a flange 7 whichcorresponds with its dimensions to a flange 8 of the casing 1. In orderto connect both flanges 7,8, only indicated fixing agents 9 are used,e.g. bolts or screws which are screwed into corresponding threaded holesin the flange 8. So that the grounding switch 3 can be utilized not onlyfor grounding purposes but also for testing purposes, the end faces 10of the flange 7 which are turned towards each other and the end faces 11of the flange 8 do not repose immediately adjacent each other, butrather, a metallic ring 12 is mounted between them which is penetratedby the fixing agents 9. The ring does not have the same width as theflanges 7 and 8 but rather is narrower.

An insulating ring 13, on the inside of which an annular electricconductor 14 is embedded, reposes within the metallic ring 12. Thisconductor 14 has a terminal lug 15 which extends out in radial directionand which penetrates the insulating ring 13 as well as the metallic ring12, whereby the opening 16 in the metallic ring 12 has a larger crosssection than the terminal lug 15 and the thus created gap is filled upby a correspondingly thin-walled insulating enclosure 17. The thicknessof this insulating enclosure 17 is dimensioned according to themagnitude of the test voltage to be applied. The conductor 14 bears onits end face 18 which is turned towards the casing 1 the sliding contact19, which contacts the contact pin 5 of the grounding switch 3. In thismanner, voltaic contact between the contact pin 5 and the conductor 14or its terminal lug 15 is provided so that either the test voltage orground potential can be transferred from the terminal lug 15 to thecontact pin 5.

The insulating ring 13 consists of cured casting resin, e.g. epoxyresin. It is prepared in that the metallic ring 12 which acts as a propring is part of a casting mold within which the conductor 14 with itsterminal lug 15 is retained correspondingly at a distance from the wallsof the casting mold or the opening 16. The conductor 14 is embedded inthe insulating ring 13 by means of the casting process and subsequentcuring of the casting resin. The insulating enclosure 17 thereby shrinksgastight onto the terminal lug 15. While assembling the insulating ring13 with the conductor 14, only a gastight sealing of the end faces 20 ofthe insulating ring 13 opposite the end face 10 of the flange 7 or theend face 11 of the flange 8 remains to be taken care of so that the SF₆cannot overflow into the surrounding outside area from inside the casing1 and the grounding switch 3. For this purpose, two sealing rings 21,22--in particular O-rings--are provided. Of these two sealing rings, thesealing ring 21 is mounted in a groove 23 in the flange 7 while thesealing ring 22 reposes in a groove 24 in the insulating ring 13.

The insulating ring 13 is fully relieved by the metallic ring 12 of thesame height from the mechanical forces presented by the fixing agents 9for fastening the housing 6 of the grounding switch 3 to the casing 1.The insulating ring 13 virtually floats between the two sealing rings21,22 within the metallic ring 12 which acts as a prop ring. Moreover,the outer surface area 25 of the insulating ring 13 is protected by thering 12 from harmful influences from outside.

What is claimed is:
 1. A metal-clad, compressed-gas insulated, highvoltage switching station having an insulated grounding switch, thegrounding switch including a housing which is mounted to a casing of apart of the switching station by at least two flanges, the switchingstation comprising:an insulating ring; a metallic ring surrounding theinsulating ring and having a height which is at least as high as theinsulating ring, the metallic ring having a radially directed openingand being mounted with the insulating ring in a gastight fit between theflanges; an annular electric conductor disposed on an inside surface ofthe insulating ring, the annular electric conductor having a centralopening which surrounds a contact pin of the grounding switch, theannular electric conductor including a sliding contact whichelectrically connects the annular electric conductor to the contractpin; a terminal lug having an insulating enclosure provided on its outersurface, the terminal lug joining the annular electric conductor andextending radially outwardly therefrom, the terminal lug extendingthrough the insulating ring and further extending through the opening inthe metallic ring; and fixing means for joining the flanges together,the fixing means extending through the flanges and the metallic ring. 2.The metal-clad, compressed-gas insulated, high-voltage switching stationaccording to claim 1, wherein the insulating comprises a cured castingresin.